In recent years, with the advancements in speed-up and energy conservation of printers and copy machines, toners having excellent low-temperature fusing ability are even more in demand. However, usually if a resin binder for a toner is formed into a low molecular compound in order to melt the resin at low temperatures, a glass transition temperature of the resin is lowered, thereby lowering in storage property.
In order to overcome this disadvantage, as a resin binder for use in a toner having a high glass transition temperature even at a low molecular weight, polyesters obtained from a carboxylic acid having an aromatic ring such as terephthalic acid or isophthalic acid as a raw material monomer are well used.
On the other hand, Patent Publication 1 discloses, as an objective of providing a thermoplastic resin having excellent heat resistance, mechanical properties, and weathering resistance, and having a sufficient molecular weight, using biomass as a raw material, a thermoplastic resin characterized in that the thermoplastic resin has a furan structure, and that the thermoplastic resin has a reducing viscosity (ηsp/C) of 0.48 dL/g or more and a terminal acid value is less than 200 μeq/g. Also, Patent Publication 2 discloses a method for producing a polyester resin containing a dicarboxylic acid unit having a furan structure.
However, the resins described in Patent Publication 1 and Patent Publication 2 are used mainly in film applications or applications for injection-molded articles, so that the resins have high crystallinity, thereby making them unsuitable as resin binders for use in toners.
In addition, Patent Publication 3 discloses, as an objective of providing a novel polyester resin, which can be used in the production of molded articles having excellent impact resistance, a polyester resin characterized in that the polyester resin has a structural unit of a specified furan ring.
However, the resin described in Patent Publication 3 also is a composition for use in molded articles, so that the resin has a high crystallinity, thereby making it unsuitable as a resin binder for use in a toner.